It is imperative to remove non-condensable gases in as complete a manner as feasible from the absorbers of chillers based on the use of aqueous lithium bromide and the like as absorbent for water vapor. Such non-condensables are generally air and hydrogen and possibly other gases like ammonia etc. The removal of the non-condensables is generally accomplished by means of water vapor pushing said non-condensables out at the bottom of the bundle of horizontal absorber tubes. The efficiency of well purged chillers compared with that of unpurged ones is higher by up to about 70%, and if certain alcohols are used as additive, the improvement can reach 100%.
As the water vapor moves downwards passing through the bundle of horizontal tubes, it condenses and its velocity decreases to about half the initial velocity at about the middle of the tube bundle. At the lower end of the tube bundle lower velocities may result in random currents, and an adequate velocity is attained by resorting to a non-uniform arrangement of the tubings.
A problem arises due to the horizontal temperature gradient from one end of the tubes to the other. This gradient depends on the number of passes of the water through the absorber. Typically a temperature rise of about 5.degree. C. of the water in the tubes take place, and in a one-pass arrangement this is the temperature gradient between the two ends of the tube. When a number of passes is employed this temperature gradient is to be divided by the number of passes.
The colder part of the tube has a greater capability of condensing water vapor than the hotter part, and thus there exists a tendency of water vapor to pass through the warmer part of the tubings and to move towards the colder part. Non-condensables are swept along with the water-vapor and thus their removal is impaired. If this process continues, non-condensables tend to accumulate and lead to a serious impairment of the efficiency of the chiller. It is an object of the present invention to overcome the drawbacks resulting from the horizontal temperature gradient of the horizontal tubes passing through the absorber.